Selective proteolysis of human type 2 deiodinase: A novel ubiquitin-proteasomal mediated mechanism for regulation of hormone activation

B. Gereben, C. Goncalves, J. W. Harney, P. R. Larsen, A. C. Bianco

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We investigated the mechanism by which T4 regulates its activation to T3 by the type 2 iodothyronine deiodinase (D2). D2 is a short- lived (t(1/2) 50 min), 31-kDa endoplasmic reticulum (ER) integral membrane selenoenzyme that generates intracellular T3. Inhibition of the ubiquitin (Ub) activating enzyme, E1, or MG132, a proteasome blocker, inhibits both the basal and substrate-induced acceleration of D2 degradation. Using a catalytically active transiently expressed FLAG-tagged-NH2-D2, we found rapid synthesis of high molecular mass (100-300 kDa) Ub-D2 conjugates that are catalytically inactive. Ub-D2 increases when cells are exposed to D2 substrate or MG132 and disappears rapidly after E1 inactivation. Fusion of FLAG epitope to the COOH terminus of D2 prolongs its half-life approximately 2.5-fold and increases the levels of active and, especially, Ub-D2. This indicates that COOH-terminal modification interferes with proteasomal uptake of Ub-D2 that can then be deubiquitinated. Interestingly, the type 1 deiodinase, a related selenoenzyme that also converts T4 to T3 but with a half-life of >12 h, is inactivated but not ubiquitinated or degraded after exposure to substrate. Thus, ubiquitination of the ER-resident enzyme D2 constitutes a specific posttranslational mechanism for T4 regulation of its own activation in the central nervous system and pituitary tissues in which D2-catalyzed T4 to T3 conversion is the major Source of intracellular T3.

Original languageEnglish (US)
Pages (from-to)1697-1708
Number of pages12
JournalMolecular Endocrinology
Issue number11
StatePublished - Jan 1 2000


ASJC Scopus subject areas

  • Molecular Biology
  • Endocrinology

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